1. Field of the Invention
The present invention relates to a selective catalytic process for preparing N-halothiosulfonamide modified polyolefins.
2. Description of Information Disclosures
N-chlorothiosulfonamide modified rubbery polymers are described in U.S. Pat. No. 3,915,907, and U.S. Pat. No. 3,970,133 (R. J. Hopper) incorporated herein by reference. The desirability and advantages of such polymers were additionally disclosed in articles authored and co-authored by R. J. Hopper (Rubber Chemistry and Technology, Vol. 49, p. 341-352 (1976) and International Conference on Advances in the Stabilization and Controlled Degradation of Polymers, Lucerne, Switzerland, May 23-25, 1984), also incorporated herein by reference.
These references describe the reaction of various N-chlorothioamides, and particularly N-chlorothio-sulfonamides with various ethylene propylene diene monomer (EPDM) rubbers in solution (see, e.g., Examples I-XII of U.S. Pat. No. 3,915,907) as well as by mixing in a Banbury.RTM. type internal mixer (Examples XIII-XVI of U.S. Pat. No. 3,915,907). Furthermore, in Example XVII of the same reference, there is disclosed in a solution reaction the use of powdered anhydrous zinc chloride (this is referred to as a catalyst in Table I, footnote g and page 346 of the cited Rubber Chemistry and Technology article). The references contain no further disclosure concerning the effect of zinc chloride nor do they suggest the use of other catalytic agents.
U.S. Pat. No. 4,820,780 (R. J. Hopper) issued Apr. 11, 1989, discloses a method of preparing a N-chlorothiosulfonamide-containing from 3 to 6 carbon atoms and a diene in the presence of a saturated aliphatic carboxylic acid containing from 6 to 30 carbon atoms, such as stearic acid. Calcium carbonate may be added to the reaction as scavenger for the HCl by-product.
U.S. Pat. No. 3,956,247 (V. R. Landi), discloses solution halogenation of a rubbery terpolymer of ethylene, an alpha mono-olefin, and a nonconjugated diene in the presence of an epoxy compound such as epoxidized soybean oil.
The addition reaction of N-halothiosulfonamides to olefins is generally thought to proceed through carbonium ion intermediates. Non-conjugated dienes, such as ethylidenenorbornene contain, after incorporation into a polymer, a fully substituted (quaternary) carbon atom. Since this permits the formation of a particularly stable tertiary carbonium ion intermediate, such non-conjugated dienes would be expected to react at high rates with halothiosulfonamides. It has now been observed that the reaction of a halothiosulfonamide with polymers containing both hexadiene and ethylidenenorbornene appears to occur almost exclusively at the latter olefin moiety. However, a disadvantage of the presence of such quaternary olefinic carbon atoms is that they facilitate dehydrohalogenation and cationic crosslinking of such polymers. Thus, although the presence of a non-conjugated diene, which after incorporation in the polymer contains a fully substituted carbon atom, leads to a rapid reaction, the presence of such a non-conjugated diene also leads to a non-selective reaction. At very low molar ratios of the halothiosulfonamide to unsaturated sites having quaternary olefinic carbon atoms and in solution at low temperatures, it is possible to obtain a selective reaction. Hopper describes, in Example IX of U.S. Pat. No. 3,915,907, the reaction of chlorothiosulfonamides with EPDM containing ethylidene-norbornene as the non-conjugated diene. The reaction is carried out with 0.01 mole of halothiosulfonamide per mole of unsaturated sites in the polymer (in contrast to his preferred range of 0.06 to 1 mole per mole of unsaturated sites in the polymer) and in solution at 25.degree. C. Hopper makes no statement as to the presence or absence of crosslinking in this product.
A process that would permit a selective reaction of N-halothiosulfonamides with polyolefins containing a non-conjugated diene having, after incorporation with the polyolefin, a quaternary olefinic carbon atom that is fully substituted, would be desirable, particularly if such a process would not need to depend on the use of low temperature (e.g., room temperature) to achieve such selectivity, thereby incuring the disadvantage of low reaction rates and, even more particularly, if such a process could be conducted in the melt phase (i.e., bulk polymer phase) of the polymer.
It has now been found that a selective reaction of N-halothiosulfonamides with polyolefin polymers comprising a diene which, after incorporation in the polymer, includes a fully substituted carbon atom, can be obtained.
By "selectivity" is intended herein that the desired addition reaction is increased while the undesired crosslinking reaction, which leads to increased Mooney viscosity and to gelation, is minimized.